1. Field of Invention
The present invention relates to methods and systems for electronic countermeasures, and particularly to methods and systems for electronic countermeasures that employ radar jamming devices.
2. Description of the Related Art
The word “radar” is an acronym for Radio Detection and Ranging that was coined by the U.S. Navy in the 1940's when the technology was in its infancy. Essentially, a radar system is one that alternately transmits radio frequency (RF) signals into a given search volume and then listens for reflections. By properly processing the radar returns, a radar system can determine the direction, range, altitude and/or speed of a target. Currently, radar is used in a wide variety of different ways. For example, weather researchers use radar to track rain and snow storms. Police use radar to determine the speed of motorists. Civil aviation uses radar for air traffic control purposes. The military uses radar to track aircraft, ships, terrain and missiles. Needless to say, this is a small list of examples.
For example, when military aircraft enter the airspace of a hostile power or nation, there is a high probability that they will come under surveillance by one or more enemy radars and thus become a target for radar guided weapons such as missiles, fighter aircraft, cannon, and other such weapons. In light of this threat, military aircraft must be equipped with effective electronic countermeasures and stealth mechanisms to prevent being detected, intercepted, and/or destroyed.
One type of countermeasure that is routinely used is commonly referred to as “jamming.” Briefly stated, jamming refers to the use of RF signals to interfere with the hostile radar system's ability to detect and track targets. The jamming signal is designed to deceive or disable the hostile radar receiver. Jamming signals may be directed toward the main radar beam or the radar side lobes. Note that a target is detected when the RF energy of the main lobe hits the target and is reflected back to the radar receiver. Thus, the jammer must be aligned with the main lobe of the radar when main lobe jamming is performed. For side lobe jamming, the jammer is off-axis and aligned with the radar side lobes. The jamming is nonetheless effective because it disrupts the radar processing and may result in the radar detecting false targets. Another type of jamming is referred to as barrage jamming in which jamming signals consist of broadband noise. In response to jamming countermeasures, radar systems are now equipped with their own counter-countermeasures to defeat various types of jamming systems as well as other sources of interference.
For example, some radar systems have “adaptive sidelobe canceling” capabilities. Often, the radar system will include an auxiliary antenna that is configured to receive and process jamming signals. Essentially, the jamming signal in the radar main antenna channel and that in the auxiliary channel are applied in determining combining weights that upon application to received signals cancels the jamming without degrading the target return signal. Another approach that is used to neutralize a jammer, and other coherent interference, is referred to as blanking. A blanker also includes a dedicated receive antenna and the object is to reduce or eliminate the effects of sidelobe signals that mimic the radar waveform. Essentially, if the processor determines that the sidelobe signal exceeds the main beam signal, the signal output obtained from the main beam is rejected (blanked).
Indeed, jammers are used as an electronic counter measure (“ECM”) technique to degrade radar sensitivity performance by effectively raising the noise floor through the sidelobes of receive beams. However, jammer energy entering through the receive beam sidelobes is particularly challenging because it varies as a function of angle relative to the jammer. This requires a separate cancellation filter to be calculated and applied for each predefined scan beam angle, and more importantly for each arbitrary track beam angle.
Description of the Related Art Section Disclaimer: To the extent that specific patents/publications/products are discussed above in this Description of the Related Art Section or elsewhere in this Application, these discussions should not be taken as an admission that the discussed patents/publications/products are prior art for patent law purposes. For example, some or all of the discussed patents/publications/products may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific patents/publications/products are discussed above in this Description of the Related Art Section and/or throughout the application, the descriptions/disclosures of which are all hereby incorporated by reference into this document in their respective entirety(ies).
Accordingly, there is a continued need for sidelobe cancellation systems and methods that account for and surmount the limitations inherent in current systems.